Salt suitable for an acid generator and a chemically amplified resist composition containing the same

ABSTRACT

The present invention provides a salt of the formula (L) A salt of the formula (L):  
                 
 
wherein Q represents —CO— group or —C(OH)— group; ring X represents monocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atoms in which a hydrogen atom is substituted with a hydroxyl group at Q position when Q is —C(OH)— group or in which two hydrogen atoms are substituted with ≡O group at Q position when Q is —CO— group, and at least one hydrogen atom in the monocylic or polycyclic hydrocarbon group may optionally be substituted with alkyl group having 1 to 6 carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkyl group having 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6 carbon atoms, hydroxyl group or cyano group; R 10  and R 20  each independently represent fluorine atom or perfluoroalkyl group having 1 to 6 carbon atoms; and A +  represents organic counter ion. 
The present invention also provides a chemically amplified resist composition comprising the salt of the formula (L).

This nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application Nos. 2005-97485 and 2006-14722 filed in JAPAN onMar. 30, 2005 and Jan. 24, 2006, the entire contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a salt suitable for an acid generatorused for a chemically amplified resist composition which is used in fineprocessing of semiconductors, and a chemically amplified resistcomposition containing the salt.

BACKGROUND OF THE INVENTION

A chemically amplified resist composition used for semiconductormicrofabrication employing a lithography process contains an acidgenerator comprising a compound generating in acid by irradiation.

In semiconductor microfabrication, it is desirable to form patternshaving improved pattern profiles and having high resolution and, and itis expected for a chemically amplified resist composition to give suchpatterns.

Recently, a chemically amplified resist composition containingtriphenylsulfonium 1-adamantanemethoxycarbonyldifluoromethansulfonate,p-tolyldiphenylsulfonium perfluorooctanesulfonate, and the like areproposed (e.g. JP2004-4561-A), and a salt providing a chemicallyamplified resist composition giving patterns having better patternprofiles and higher resolution.

SUMMARY OF THE INVENTION

Objects of the present invention are to provide a salt suitable for anacid generator capable of providing chemically amplified resistcompositions giving patterns having better resolution and havingimproved pattern profiles and a process for producing the salt.

Another objects of the present invention are to provide syntheticintermediates for the salts and to provide a process for producing thesynthetic intermediates or the salts.

Still another object of the present invention are to provide achemically amplified resist composition containing the salts.

These and other objects of the present invention will be apparent fromthe following description.

The present invention relates to the followings:<1> A salt of the formula (L):

wherein Q represents —CO— group or —C(OH)— group; ring X representsmonocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atomsin which a hydrogen atom is substituted with a hydroxyl group at Qposition when Q is —C(OH)— group or in which two hydrogen atoms aresubstituted with ≡O group at Q position when Q is —CO— group, and atleast one hydrogen atom in the monocyclic or polycyclic hydrocarbongroup may optionally be substituted with alkyl group having 1 to 6carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkylgroup having 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰ eachindependently represent fluorine atom or perfluoroalkyl group having 1to 6 carbon atoms; and A⁺ represents organic counter ion. Hereinafter,the salt of the formula (L) may be referred to as Salt (L).<2> The salt according to <1>, wherein each of R¹⁰ and R²⁰ is fluorineatom or trifluoromethyl group.<3> The salt according to <1> or <2>, wherein the salt has the followingformula (I)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined above.<4> The salt according to <1> or <2>, wherein the salt has the followingformula (II)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined above.<5> The salt according to any of <1> to <4>, wherein A⁺ is at least onecation selected from the group consisting of the formula (IIIa), theformula (IIIb), the formula (IIIc) and the formula (IIId).A cation of the formula (IIIa)

wherein P¹, P² and P³ each independently represent hydrogen atom,hydroxyl group, alkyl group having 1 to 12 carbon atoms or alkoxy grouphaving 1 to 12 carbon atoms.A cation of the formula (IIIb)

wherein P⁴ and P⁵ each independently represent hydrogen atom, hydroxylgroup, alkyl group having 1 to 12 carbon atoms or alkoxy group having 1to 12 carbon atoms.The formula (IIIc)

wherein P⁶ and P⁷ each independently represent alkyl having 1 to 12carbon atoms or cycloalkyl having 3 to 12 carbon atoms, or P⁶ and P⁷bond to form divalent acyclic hydrocarbon group having 3 to 12 carbonatoms which forms a ring together with the adjacent S⁺, and at least one—CH₂— in the divalent acyclic hydrocarbon group is optionallysubstituted by —CO—, —O— or S—, P⁸ represents hydrogen, P⁹ representsalkyl having 1 to 12 carbon atoms, cycloalkyl having 3 to 12 carbonatoms or aromatic ring group optionally substituted, or P⁸ and P⁹ bondto form divalent acyclic hydrocarbon group which forms 2-oxocycloalkyltogether with the adjacent —CHCO—, and at least one —CH₂— in thedivalent acyclic hydrocarbon group is optionally substituted by —CO—,—O— or —S—.A cation of the formula (IIId)

wherein P¹⁰, P¹¹, P¹², P¹³, P¹⁴, P¹⁵, P¹⁶, P¹⁷, P¹⁸, P¹⁹, P²⁰ and P²¹each independently represent hydrogen atom, hydroxyl group, alkyl grouphaving 1 to 12 carbon atoms or alkoxy group having 1 to 12 carbon atoms,B represents sulfur atom or oxygen atom, and m represents 0 or 1.<6> The salt according to any of any of <1> to <5>, wherein A′ is acounter ion of the formula (IIIe):

wherein P²², P²³ and P²⁴ each independently represent hydrogen atom oralkyl group having 1 to 4 atoms.<7> The salt according to any of <1> to <6>, wherein the ring X iscycloalkyl group having 4 to 8 carbon atoms, adamantyl group or norbonylgroup, provided that, in each of the group, a hydrogen atom issubstituted with —OH group at Q position when Q is —C(OII)— group andtwo hydrogen atoms are substituted with ≡O at Q position when O is —CO—group, and provided that at least one hydrogen atom in each of the groupmay optionally be substituted with alkyl group having 1 to 6 carbonatoms, alkoxy group having 1 to 6 carbon atoms, perfluoroalkyl grouphaving 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6 carbonatoms, hydroxyl group or cyano group.<8> The salt according to <6>, wherein the salt is the one of theformula (IVa)

wherein P²⁵, P²⁶ and P²⁷ each independently represent hydrogen atom,alkyl group having 1 to 4 carbon atom.<9> The salt according to <6>, wherein the salt is the one of theformula (IVa)

wherein P²⁵, P²⁶ and P²⁷ have the same meanings as defined above.<10> A salt of the formula (LI)

wherein Q, X, R¹⁰ and R²⁰ have the same meanings as defined above, and Mrepresents Li, Na, K or Ag.<11> The salt according to <10>, wherein the salt has the formula (V)

wherein X, R¹⁰, R²⁰ and M have the same meanings as defined above.<12> The salt according to <10>, wherein the salt has the formula (VI)

wherein X, R¹⁰, R²⁰ and M have the same meanings as defined above.<13> A process for producing a salt of the formula (LI), which comprisesesterifying an alcohol of the formula (LII)

wherein X and Q have the same meanings as defined above, with acarboxylic acid or the formula (IX)

wherein R¹⁰, R²⁰ and M have the same meanings as defined above.<14> A process for producing a salt of the formula (II), which comprisesreducing a salt of the formula (I).<15> A process for producing a salt of the formula (VI), which comprisesreducing a salt of the formula (V).<16> A process for producing a salt of the formula (LI), which comprisesesterifying an alcohol of the formula (LII) with a caboxylic acid of theformula (X)

wherein R¹⁰ and R²⁰ have the same meanings as defined above, andhydrolyzing with MOH,wherein M has the same meaning as defined above.<17> A process for producing Salt (L), which comprises reacting a saltof the formula (LI) with a compound of the formula (XI)A³⁰ Z⁻  (XI)wherein Z represents F, Cl, Br, I, BF₄, AsF₆, SbF₆, PF₆ or ClO₄, and A⁺has the same meaning as defined above.<18> A chemically amplified resist composition comprisingSalt (L) anda resin which contains a structural unit having an acid-labile group andwhich itself is insoluble or poorly soluble in an alkali aqueoussolution but becomes soluble in an alkali aqueous solution by the actionof an acid.<19> The composition according to <18>, wherein each of R¹⁰ and R²⁰ isfluorine atom or trifluoromethyl group.<20> The composition according to <18> or <19>, wherein the resincontains a structural unit derived from a monomer having a bulky andacid-labile group.<21> The composition according to <20>, wherein the bulky andacid-labile group is 2-alkyl-2-adamantyl group or1-(1-adamantyl)-1-alkylalkyl group.<22> The composition according to <20>, wherein the monomer having bulkyand acid labile group is 2-alkyl-2-adamantyl (meth)acrylate,1-(1-adamantyl)-1-alkylalkyl (meth)acrylate, 2-alkyl-2-adamantyl5-norbornene-2-carboxylate, 1-(1-adamantyl)-1-alkylalkyl5-norbornene-2-caraboxylate, 2-alkyl-2-adamantyl α-chloroacrylate or1-(1-adamantyl)-1-alkylalkyl α-chloroacrylate.<23> The composition according to any of <18> to <22>, wherein thecomposition further comprises a basic compound.<24> The salt according to any of <18> to <23>, wherein the salt is theone of the formula (I).<25> The composition according to any of <18> to <23>, wherein the saltis the one of the formula (II).<26> The composition according to any of <18> to <25>, wherein A⁺ is atleast one cation selected from the group consisting of the formula(IIIa), the formula (IIIb), the formula (IIIc) and the formula (IIId).<27> The composition according to <26>, wherein A⁺ is a counter ion ofthe formula (IIIe).<28> The composition according to any of <18> to <27>, wherein the ringX is cycloalkyl group having 4 to 8 carbon atoms, adamantyl group ornorbornyl group, provided that, in each of the group, a hydrogen atom issubstituted with —OH group at Q position when Q is —C(OH)— group and twohydrogen atoms are substituted with ≡O at Q position when Q is —CO—group, and provided that at least one hydrogen atom in each of the groupmay optionally be substituted with alkyl group having 1 to 6 carbonatoms, alkoxy group having 1 to 6 carbon atoms, perfluoroalkyl grouphaving 1 to 4 carbon atoms, hydroxylalkyl group having 1 to 6 carbonatoms, hydroxyl group or cyano group.<29> The composition according to <27>, wherein the salt is the one ofthe formula (IVa).<30> The composition according to <27>, wherein the salt is the one ofthe formula (IVb).

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is the ¹H-NMR spectrum chart of triphenylsulfonium4-hydroxy-1-adamantyloxycarbonyldifluoromethanesulfonate produce inSynthetic Example 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

In Salt (L), Q represents —CO— group of —C(OH)— group. When Q is —CO—group, the salt is Salt (I), and when Q is —C(OH)— group, the salt isSalt (II).

When Q is —CO— group, the ring X represents monocyclic or polycyclichydrocarbon group having 3 to 30 carbon atoms in which two hydrogenatoms at Q position are substituted with ≡O. When Q is —C(OH)— group,the ring X represents a monocyclic or polycyclic hydrocarbon grouphaving 3 to 30 carbon atoms in which a hydrogen atom at Q position issubstituted with a hydroxyl group. At least one hydrogen atom in themonocyclic or polycyclic hydrocarbon group may optionally be substitutedwith alkyl group having 1 to 6 carbon atom, alkoxy group having 1 to 6carbon atom, perfluoroalkyl group having 1 to 4 carbon atoms,hydroxyalkyl group having 1 to 6 carbon atoms, hydroxyl group or cyanogroup.

Examples of the ring X include cycloalkyl group having 4 to 8 carbonatoms, adamantyl group or norbornyl group, wherein, in each of thecycloalkyl group, adamantyl group and norbornyl group, a hydrogen atomis substituted with —OH group at Q position when Q is —C(OH)— group andtwo hydrogen atoms are substituted with ≡O at Q position when Q is —CO—group, and at least one hydrogen atom in each of the cycloakkyl group,adamantyl group and norbornyl group may optionally be substituted withalkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6carbon atoms, perfluoroalkyl group having 1 to 4 carbon atoms,hydroxyalkyl group having 1 to 6 carbon atoms, hydroxyl group or cyanogroup.

Specific examples of the ring X include 2-oxocyclopentyl group,2-oxocyclohexyl group, 3-oxocyclopentyl group, 3-oxocyclohexyl group,1-oxocyclohexyl group, 2-hydroxycyclopentyl group, 2-hydroxycyclohexylgroup, 3-hydroxycyclopentyl group, 3-hydroxycyclohexyl group,4-hydroxycyclohexyl group, 4-oxo-2-adamantyl group,3-hydroxy-1-adamantyl group, 4 hydroxy-1-adamantyl group,5-oxonorbornan-2-yl group, 1,7,7-trimethyl-2-xonorbornan-2-yl group,3,6,6-trimethyl-2-oxo-bicyclo[3.1.1]heptan-3-yl group,2-hydroxy-norbornan-3-yl group, 1,7,7-trimethyl-2-hydroxynorbornan-3ylgroup, 3,6,6-trimethyl-2-hydroxybicyclo[3.1.1]heptan-3-yl group.

and the like.In the formulae above, straight line with an open end shows a bond whichis extended from an adjacent group.

R¹⁰ and R²⁰ each independently represent fluorine atom or perfluoroalkylgroup having 1 to 6 carbon atoms such as trifluoromethyl group,pentafluoroethyl group, heptafluoropropyl group, nonafluorobutyl group,undecafluoropentyl group, tridecafluorohexyl group, and the like.

Specific examples of anion part of the salt (L) include the followings.

A⁺ in Salt (L) represents an organic counter ion. Examples thereofinclude the following cations of the formulae (IIIa), (IIIb), (IIIc) and(IIId).

In the cation of the formula (IIIa), P¹, P² and P³ each independentlyrepresent hydrogen atom, hydroxyl group, alkyl group having 1 to 12carbon atoms or alkoxy group having 1 to 12 carbon atoms.

Examples of the alkyl group in the formula (IIIa) include methyl group,ethyl group, propyl group, isopropyl group, butyl group, tert-butylgroup, pentyl group, hexyl group, octyl group, 2-ethylhexyl group, andthe like, and examples of the alkoxy group include methoxy group, ethoxygroup, propoxy group, butoxy group, hexyloxy group, octyloxy group,2-ethylhexyloxy group, and the like.

In the cation of the formula (IIIa), the one of the formula (IIIe) aboveis preferred for the easiness of production.

In the cation of the formula (IIIb), P⁴ and P⁵ each independentlyrepresent hydrogen atom, hydroxyl group, alkyl group having 1 to 12carbon atoms or alkoxy group having 1 to 12 carbon atoms. Examples ofthe alkyl group and alkoxy group include the same groups as mentioned inthe formula (IIIa) above.

In the cation of the formula (IIIc), P⁶ and P⁷ each independentlyrepresent alkyl having 1 to 12 carbon atoms or cycloalkyl having 3 to 12carbon atoms, or P⁶ and P⁷ bond to form divalent acyclic hydrocarbongroup having 3 to 12 carbon atoms which forms a ring together with theadjacent S⁺, and at least one —CH₂— in the divalent acyclic hydrocarbonmay be substituted by —CO—, —O— or —S—.

P⁸ represents hydrogen, P⁹ represents alkyl having 1 to 12 carbon atoms,cycloalkyl having 3 to 12 carbon atoms or aromatic ring group optionallysubstituted, or P⁸ and P⁹ bond to form divalent acyclic hydrocarbongroup which forms 2-oxocycloalkyl together with the adjacent —CHCO—, andat least one —CH₂— in the divalent acyclic hydrocarbon group may besubstituted by —CO—, —O— or —S—.

In P⁶, P⁷ and P⁹, specific examples of the alkyl group include methylgroup, ethyl group, propyl group, isopropyl group, butyl group,tert-butyl group, pentyl group, hexyl group, and the like, and specificexamples of the cycloalkyl group include cyclopropyl group, cyclobutylgroup, cyclopentyl group, cyclohexyl group, cycloheptyl group,cyclodecyl group, and the like. Specific examples of the divalentacyclic hydrocarbon group having 3 to 12 carbon atoms formed by bondingP⁶ and P⁷ include methylene group, ethylene group, trimethylene group,tetramethylene group, pentamethylene group, and the like, and specificexamples of the ring group formed by adjacent S⁺ and divalent acyclichydrocarbon group by P⁶ and P⁷ include pentamethylenesulfonio group,tetramethylenesulfonio group, oxybisethylenesulfonio group, and thelike. In P⁹, specific examples of the aromatic ring group includephenyl, tolyl, xylyl, naphtyl and the like. Specific examples of thedivalent acyclic hydrocarbon group formed by bonding P⁸ and P⁹ includemethylene group, ethylene group, oimethylene group, tetramethylenegroup, pentamethylene group, and the like, and specific examples of the2-oxocycloalkyl formed by bonding P⁸ and P⁹ together with the adjacent—CHCO— include 2-oxocyclohexyl, 2-oxocyclopentyl and the like.

In the cation of the formula (IIId), P¹⁰, P¹¹, P¹², P¹³, P¹⁴, P¹⁵, P¹⁶,P¹⁷, P¹⁸, P¹⁹, P²⁰ and P²¹ each independently represent hydrogen atom,hydroxyl group, alkyl group having 1 to 12 carbon atoms or alkoxy grouphaving 2 to 12 carbon atoms, B represents sulfur atom or oxygen atom,and m represents 0 or 1. Examples of the alkyl group and alkoxy groupinclude the same groups as mentioned in the formula (IIIa) above.

Specific examples of the formula (IIIb) include the following:

Specific examples of the formula (IIIc) include the following:

Specific examples of the cation of the formula (IIId) include thefollowing:

As Salt (L), the salts of the formulae (IVa) and (IVb) are preferred forthe excellent resolution and pattern profile.

In the formulae (IVa) and (IVb), P²⁵, P²⁶ and P²⁷ each independentlyrepresent hydrogen atom or alkyl group having 1 to 4 carbon atom.

Examples of the process for production of Salt (L) include a processcomprising reacting a salt of the formula (LI) with a compound of theformula (XI), for example, in an inert solvent such as acetonitrile,water, methanol, dichloromethane, and the like, at a temperature ofabout 0 to 150, preferably of 0 to 100° C., with stirring.

The amount of the compound of the formula (XI) is usually 0.5 to 2 molsper 1 mol of the salt of the formula (LI). Salt (L) obtained by theprocess above can be isolated by recrystallization, and can be purifiedby washing with water.

The salt of the formula (LI) used for the production of Salt (L) can beproduced for example, by a process comprising esterifying an alcohol ofthe formula (LII) with a carboxylic acid of the formula (IX).

When Q is —CO—, the alcohol of the formula (LII) is an alcohol of theformula (VII)

wherein X has the same meaning as defined above, andwhen Q is —C(OH)—, the alcohol of the formula (LII) is an alcohol of theformula (VIII)

wherein X has the same meaning as defined above.

The esterification reaction can generally be carried out by mixingmaterials in an aprotic solvent such as dichloromethane, toluene,ethylbenzene, monochlorobenzene, acetonitrile, N,N-dimethylformamide,and the like, at 20 to 200° C. preferably 50 to 150° C. In theesterification reaction, an acid catalyst or a dehydrating agent isusually added, and examples of the acid catalyst include organic acidssuch as p-toluenesulfonic acid, inorganic acids such as sulfuric acid,and the like. Examples of the dehydrating agent include1,1′-carbomyldiimidazole, N,N′-dicyclohexylcarboiimide, and the like.

The esterification may preferably be carried out with dehydration, forexample, by Dean and Stark method as the reaction time tends to beshortened.

The amount of the carboxylic acid of the formula (IX) is usually 0.2 to3 mol, preferably 0.5 to 2 mol per 1 mol of the alcohol of the formula(LII). The amount of the acid catalyst may be catalytic amount or theamount equivalent to solvent, and is usually 0.001 to 5 mol per 1 mol ofthe alcohol of the formula (LII). The amount of the dehydrating agent isusually 0.2 to 5 mol, preferably 0.5 to 3 mol per 1 mol of the alcoholof the formula (LII).

The salt of the formula (LI) can also be produced by a processcomprising esterifying the alcohol of the formula (LII) with acarboxylic acid of the formula (X), then hydrolyzing the esterifiedcompound with MOH, wherein M represents Li, Na, K or Ag. Theesterification reaction can be carried out in the same manner as in theesterification of the alcohol of the formula (LII) with carboxylic acidof the formula (IX). The hydrolyzation reaction can usually be carriedout by stirring a mixture of the esterified compound obtained by theesterification reaction and MOH in a solvent. The solvent may be wateror a mixed solvent of water and water-soluble solvent such asacetonitrile, tetrahydrofuran, and the like. The end point of thereaction can be determined, for example, by the analysis of ¹⁹FNMR. Theamount of the carboxylic acid of the formula (X) is usually 0.2 to 3mol, preferably 0.5 to 2 mol per 1 mol of the alcohol of the formula(LII). The amount of the acid catalyst may be catalytic amount or theamount equivalent to solvent, and is usually 0.001 to 5 mol per 1 mol ofthe alcohol of the formula (LII). The amount of the dehydrating agent isusually 0.2 to 5 mol, preferably 0.5 to 3 mol per 1 mol of the alcoholof the formula (LII).

The amount of the MOH is usually 0.2 to 3 mol, preferably 1 to 2 mol per1 mol of the ester.

The salt of the formula (II) can also be produced by reducing the saltof the formula (I), and similarly the salt of the formula (VI) can alsobe produced by reducing the salt of the formula (V).

The reduction reaction can be carried out by using reducing agents suchas boron hydride compounds (e.g. sodium borohydride, zinc borohydride,lithium trisec.-butylborohydride, borane, and the like), aluminumhydride compound (e.g. lithium tri-tert-butoxyaluminum hydride,diisobutylaluminum hydride, and the like), organosilicon hydridecompound (e.g. Et₃SiH, Ph₂SiH₂, and the like), and the like, in asolvent such as water, alcohol, acetonitrile, N,N-dimethylformamide,diglyine, tetrahydrofuran, diethyl ether, dichloromethane,1,2-dimethoxyethane, benzene, and the like. Reaction is usually carriedout at a temperature of −80° to +100° C., preferably at −10 to +60° C.with stirring.

The present chemically amplified resist composition comprises Salt (L)and a resin which contains a structural unit having an acid-labile groupand which itself is insoluble or poorly soluble in an alkali aqueoussolution but becomes soluble in an alkali aqueous solution by the actionof an acid.

Salt (L) is usually used as an acid generator, and the acid generated byirradiation to Salt (L) catalytically acts against acid-labile groups ina resin, cleaves the acid-labile group, and the resin becomes soluble inan alkali aqueous solution. Such a composition is suitable forchemically amplified positive resist composition.

The resin used for the present composition contains a structural unithaving an acid-labile group and which itself is insoluble or poorlysoluble in an alkali aqueous solution, but acid-labile group cleave byan acid. The resin after the cleavage contains carboxylic acid residueand as a result, the resin becomes soluble in an alkali aqueoussolution.

In the present specification, “—COOR” may be described as “a structurehaving ester of carboxylic acid”, and may also be abbreviated as “estergroup”. Specifically, “—COOC(CH₃)₃” may be described as “a structurehaving tert-butyl ester of carboxylic acid”, or be abbreviated as“tert-butyl ester group”.

Examples of the acid-labile group include a structure having ester ofcarboxylic acid such as alkyl ester group in which a carbon atomadjacent to the oxygen atom is quaternary carbon atom, and alicyclicester group in which a carbon atom adjacent to the oxygen atom isquaternary carbon atom, and the like, a lactone ring group in which acarbon atom adjacent to the oxygen atom is quaternary carbon atom, andthe like.

The “quaternary carbon atom” means a “carbon atom joined to foursubstituents other than hydrogen atom”. As the acid-labile group, agroup having a quaternary carbon atom joined to three carbon atoms, anda OR′, wherein R′ represents alkyl group.

Examples of the acid-labile group include alkyl ester group in which acarbon atom adjacent to the oxygen atom is quaternary carbon atom suchas tert-butyl ester group; acetal type ester group such as methoxymethylester group, ethoxymethyl ester group, 1-ethoxyethyl ester group,1-isobutoxyethyl ester group, 1-isopropoxyethyl ester group,1-ethoxypropoxy ester group, 1-(2-methoxyethoxy)ethyl ester,1-(2-acetoxyethoxy)ethyl ester group, 1-[2-(1-adamantyloxy)ethoxy]ethylester group, 1-[2-(1-adamantanecarbonyloxy)ethoxy]ethyl ester group,tetrahydro-2-furyl ester and tetrahydro-2-pyranyl ester group; alicyclicester group in which a carbon atom adjacent to the oxygen atom isquaternary carbon atom, such as isobornyl ester group, 1-alkylcycloalkylester group, 2-alkyl-2-adamantyl ester group,1-(1-adamantyl-1-alkylalkyl ester group, and the like.

Examples of structures including the ester group include ester of(meth)acrylic acid structure, ester of norbornenecarboxylic acidstructure, and the like. At least one hydrogen atom in the adamantylgroup above may be substituted by hydroxyl group.

The resin used for the present composition can be obtained by additionpolymerization of monomer(s) having an acid-labile group and olefinicdouble bond.

Among the monomers, it is preferable to use those having a bulky groupsuch as alicyclic group (e.g. 2-alkyl-2-adamantyl and1-(1-adamantyl)-1-alkylalkyl), as the group dissociated by the action ofan acid, since excellent resolution is obtained when used in the presentcomposition.

Examples of such monomer containing a bulky group include2-alkyl-2-adamantyl (meth)acrylate, 1-(1-adamantyl-1-alkylalkyl(meth)acrylate, 2-alkyl-2-adamantyl 5-norbornene-2-carboxylate,1-(1-adamantyl)-1-alkylalkyl 5-norbornene-2-carboxylate,2-alkyl-2-adamantyl α-chloroacrylate, 1-(1-adamantyl)-1-alkylalkylα-chloroacrylate and the like.

Particularly when 2-alkyl-2-adamantyl (meth)acrylate or2-alkyl-2-adamantyl α-chloroacrylate, is used as the monomer for theresin component in the present composition, resist composition havingexcellent resolution tend to be obtained. Typical examples of such2-alkyl-2-adamantyl (methy)acrylate and 2-alkyl-2-adamantylα-chloroacrylate include 2-methyl-2-adamantyl acrylate, 2methyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl acrylate,2-ethyl-2-adamantyl methacrylate, 2-n-butyl-2-adamantyl acrylate,2-methyl-2-adamantyl α-chloroacrylate, 2-ethyl-2 adamantylα-chloroacrylate and the like. When particularly 2-ethyl-2-adamantyl(meth)acrylate or 2-isopropyl-2-adamantyl (meth)acrylate is used for thepresent composition, composition having excellent sensitivity and heatresistance tends to be obtained. In the present invention, two or morekind of monomers, having group dissociated by the action of an acid maybe used together, if necessary.

2-Alkyl-2-adamantyl (meth)acrylate can usually be produced by reacting2-alkyl-2-adamantanol or metal salt thereof with an acrylic halide ormethacrylic halide.

The resin used for the present composition can also contain, in additionto the above-mentioned structural units having an acid-labile group,other structural unit derived from acid-stable monomer. Herein, the“structural unit derived from acid-stable monomer” means “a structuralunit not dissociated by an acid generated from Salt (L)”.

Examples of such other structural units which can be contained includestructural units derived from monomers having a free carboxyl group suchas acrylic acid and methacrylic acid, structural units derived fromaliphatic unsaturated dicarboxylic anhydrides such as maleic anhydrideand itaconic anhydride, structural units derived from 2-norbornene,structural units derived from (meth)acrylonitrile, structural unitsderived from alkyl (meth)acrylate in which a carbon atom adjacent tooxygen atom is secondary or tertiary carbon atom, structural unitsderived from 1-adamantyl(meth)acrylate; structural units derived fromstyrenes such as p- or m-hydroxystyrene, structural units derived from(methy)acryloyloxy-γ-butyrolactone having a lactone ring optionallysubstituted by alkyl, and the like. Herein, 1-adamantyl ester group is aacid-stable group though the carbon atom adjacent to oxygen atom isquaternary carbon atom, and at least one hydrogen atom on 1-adamantyester group may be substituted by hydroxy group.

Specific examples of structural unit derived from acid-stable monomerinclude a structural unit derived from 3-hydroxyl-1-adamantyl(meth)acrylate, a structural unit derived from 3,5-dihydroxy-1-adamantyl(meth)acrylate, a structural unit derived fromα-(meth)acryloyloxy-γ-butyrolactone, a structural unit derived fromβ-(meth)acryloyloxy-γ-butyrolactone, a structural unit of the followingformula (a), a structural unit derived from the following formula (b), astructural unit derived from alicyclic compound having olefinic doublebond such as a structural unit of the following formula (c), astructural unit derived from aliphatic unsaturated dicarboxylicanhydride such as a structural unit of the formula (d), a structuralunit of the formula (e), and the like.

Particularly, to contain, in addition to the structural unit having anacid-labile group, further at least one structural unit selected fromthe group consisting of a structural unit derived from p hydroxystyrene,a structural unit derived from m-hydroxystyrene, a structural unitderived from 3-hydroxy-1-adamantyl (meth)acrylate, a structural unitderived from 3,5 dihydroxy-1-adamantyl (meth)acrylate, a structural unitof the following formula (a) and a structural unit of the followingformula (b), in the resin in the present composition, is preferable fromthe standpoint of the adhesiveness of resist to a substrate andresolution of resist.

In the formulae (a) and (b), R¹ and R² each independently representhydrogen atom, methyl group or trifluoromethyl group and R³ and R⁴ eachindependently represent methyl group, trifluoromethyl group or halogenatom, and p and q each independently represent an integer of 0 to 3.When p represents 2 or 3, each of the R³ may be the same or differentand when q represents 2 or 3, each of the R⁴ may be the same ordifferent.

3-Hydroxy-1-adamantyl (meth)acrylate and 3,5-dihydroxy-1-adamantyl(meth)acrylate can be produced, for example, by reacting correspondinghydroxyadamantane with (meth)acrylic acid or its acid halide, and theyare also commercially available.

Further, (meth)acryloxloxy-γ-butyrolactone having a lactone ringoptionally substituted by alkyl can be produced by reactingcorresponding α- or β-bromo-γ-butyrolactone with acrylic acid ormethacrylic acid, or reacting corresponding α- or β-hydroxyγ-butyrolactone with acrylic halide or methacrylic halide.

As monomers to give structural units of the formulae (a) and (b),specifically listed are, for example, (meth)acrylates of a alicycliclactones having a hydroxyl described below, and mixtures thereof, andthe like. These esters can be produced, for example, by reactingcorresponding alicyclic lactone having hydroxyl with (meth)acrylicacids, and the production method thereof is described in, for example,JP2000-26446-A.

Examples of the (meth)acryloyloxy-γ-butyrolactone having a lactone ringoptionally substituted by alkyl include α-acryloyloxy-γ-butyrolactone,α-methacryloyloxy-γ-butyrolactone,α-acryloyloxy-β,β-dimethyl-γ-butyrolactone, α-methacryloyloxy-β,βdimethyl-γ-butyrolactone, α-acryloyloxy-α-methyl-γ-butyrolactone, αmethacryloyloxy-α-methyl-γ-butyrolactone, β-acryloyloxy-γ-butyrolactone,β-methacryloyloxy-γ-butyrolactone,β-methacryloyloxy-α-methyl-γ-butyrolactone and the like.

In the case of KrF lithography, even in the case of using a structureunit derived from hydroxystyrene such as p- and m-hydroxystyrene, as oneof the resin components, resist composition having sufficienttransparency can be obtained. For obtaining such copolymerizaationresins, the corresponding (meth)acrylic ester monomer can beradical-polymerized with acetoxystyrene and styrene, and then theacetoxy group in the structure unit derived from acetoxystyrene can bede-acetylated with an acid.

The resin containing a structural unit derived from 2-norbornene showsstrong structure because alicyclic group is directly present on its mainchain and shows a property that dry etching resistance is excellent. Thestructural unit derived from 2-norbornene can be introduced into themain chain by radical polymerization using, for example, in addition tocorresponding 2-norbornene, aliphatic unsaturated dicarboxylicanhydrides such as maleic anhydride and itaconic anhydride together. Thestructural unit derived from 2-norbornene is formed by opening of itsdouble bond, and can be represented by the formula (c). The structuralunit derived from maleic anhydride and the structural unit derived fromitaconic anhydride which are the structural unit derived from aliphaticunsaturated dicarboxylic anhydrides are formed by opening of theirdouble bonds, and can be represented by the formula (d) and the formula(e), respectively.

Here, R⁵ and R⁶ in the formula (c) each independently representhydrogen, alkyl having 1 to 3 carbon atoms, hydroxyalkyl having 1 to 3carbon atoms, carboxyl, cyano or —COOU group in which U representsalcohol residue, or R⁵ and R⁶ can bond together to form a carboxylicanhydride residue represented by —C(≡O)OC(≡O)—.

In R⁵ and R⁶, examples of the alkyl include methyl, ethyl, propyl andisopropyl, specific examples of hydroxyalkyl include hydroxymethyl,2-hydroxyethyl and the like.

In R⁵ and R⁶, —COOU group is an ester formed from carboxyl, and as thealcohol residue corresponding to U, for example, optionally substitutedalkyls having about 1 to 8 carbon atoms, 2-oxooxolan-3- or -4-yl and thelike are listed, and as the substituent on the alkyl, hydroxyl,alicyclic hydrocarbon residues and the like are listed.

Specific examples of the monomer used to give the structural unitrepresented by the formula (c) may include the followings;

2-norbornene,

2-hydroxy-5-norbornene,

5-norbornen-2-carboxylic acid,

methyl 5-norbornen-2-carboxylate,

2 hydroxyethyl-5-norbornene-2-carboxylate,

5-norbornen-2-methanol,

5-norbornen-2,3-dicarboxylic acid anhydride, and the like.

When U in —COOU is acid-labile group, the structural unit of the formula(c) is a structural unit having acid labile group even if it hasnorbornene structure. Examples of monomers giving structural unit havingacid-labile group include t-butyl 5-norbornen-2-carboxylate,1-cyclohexyl-1-methylethyl 5 norbornen-2-carboxylate, 1-methylcyclohexyl5-norbornen-2-carboxylate, 2-methyl-2-adamantyl5-norbornen-2-carboxylate, 2-ethyl-2-adamantyl5-norbornen-2-carboxylate, 1-(4-methylcyclohexyl)-1-methylethyl5-norbornen-2-carboxylate, 1-(4-hydroxylcyclohexyl)-1-methylethyl5-norbornen-2-carboxylate, 1-methyl 1-(4-oxocyclohexyl(ethyl5-norbornen-2-carboxylate, 1-(1-adamantyl)-1-methylethyl5-norbornen-2-carboxylate, and the like.

The resin used in the present composition preferably contains structuralunits(s) having an acid-labile group generally in a ratio of 10 to 80%by mol in all structural units of the resin though the ratio variesdepending on the kind of radiation for patterning exposure, the kind ofan acid-labile group, and the like.

When the structural units particularly derived from 2-alkyl-2-adamantyl(meth)acrylate or 1-(1-adamantyl)-1-alkylalkyl (meth)acrylate are usedas the acid-labile group, it is advantageous that the ratio of thestructural units is 15% by mol or more in all structural units of theresin.

When, in addition to structural units having an acid-labile group, otherstructural units having acid-stable group are contained, it ispreferable that the sum of these structural units is in the range of 20to 90% by mol based on all structural units of the resin.

When alicyclic compound having olefinic double bond and aliphaticunsaturated dicarboxylic anhydride are used as copolymerization monomer,it is preferable to use them in excess amount in view of a tendency thatthese are not easily polymerized.

In the present composition, performance deterioration caused byinactivation of acid which occurs due to post exposure delay can bediminished by adding basic compounds, particularly, basic nitrogencontaining organic compounds, for example, amines as a quencher.

Specific examples of such basic nitrogen-containing organic compoundsinclude the ones represented by the following formulae:

In the formulas, T¹² and T¹³ each independently represent a hydrogenatom, an alkyl group, a cycloalkyl group or an aryl group. The alkylgroup preferably has about 1 to 6 carbon atoms, the cycloalkyl grouppreferably has about 5 to 10 carbon atoms, and the aryl group preferablyhas about 6 to 10 carbon atoms. Furthermore, at least one hydrogen atomon the alkyl group, cyloalkyl group or aryl group may each independentlybe substituted with hydroxyl group, amino group, or alkoxy group having1 to 6 carbon atoms. At least one hydrogen atom on the amino group mayeach independently be substituted with alkyl group having 1 to 4 carbonatoms.

T¹⁴, T¹⁵ and T¹⁶ each independently represent a hydrogen atom, an alkylgroup, a cycloalkyl group, an aryl group or an alkoxy group. The alkylgroup preferably has about 1 to 6 carbon atoms, the cycloalkyl grouppreferably has about 5 to 10 carbon atoms, the aryl group preferably hasabout 6 to 10 carbon atoms, and the alkoxy group preferably has about 1to 6 carbon atoms. Furthermore, at least one hydrogen atom on the alkylgroup, cycloalkyl group, aryl group or alkoxy group may eachindependently be substituted with hydroxyl group, amino group, or alkoxygroup having 1 to 6 carbon atoms. At least one hydrogen atom on theamino group may be substituted with alkyl group having 1 to 4 carbonatoms.

T¹⁷ represents an alkyl group. The alkyl group preferably has about 1 to6 carbon atoms, and the cycloalkyl group preferably has about 5 to 10carbon atoms. Furthermore, at least one hydrogen atom on the alkyl groupor cycloalkyl group may each independently be substituted with hydroxylgroup, amino group, or alkoxy group having 1 to 6 carbon atoms. At leastone hydrogen atom on the amino group may be substituted with alkyl grouphaving 1 to 4 carbon atoms.

In the formulas, T¹⁸ represents an alkyl group, a cycloalkyl group or anaryl group. The alkyl group preferably has about 1 to 6 carbon atoms,the cycloalkyl group preferably has about 5 to 10 carbon atoms, and thearyl group preferably has about 6 to 10 carbon atoms. Furthermore, atleast one hydrogen atom on the alkyl group, cycloalkyl group or arylgroup may each independently be substituted with a hydroxyl group, anamino group, or an alkoxy group having 1 to 6 carbon atoms. At least onehydrogen atom on the amino group may each independently be substitutedwith alkyl group having 1 to 4 carbon atoms.

However, none of T¹² and T¹³ in the compound represented by the aboveformula [3] is a hydrogen atom.

A represents alkylene group, carbonyl group, imino group, sulfide groupor disulfide group. The alkylene group preferably has about 2 to 6carbon atoms.

Moreover, among T¹²-T¹⁸, in regard to those which can bestraight-chained or branched, either of these may be permitted.

T¹⁹, T²⁰ and T²¹ each independently represent a hydrogen atom, an alkylgroup having 1 to 6 carbon atoms, an aminoalkyl group having 1 to 6carbon atoms, a hydroxyalkyl group having 1 to 6 carbon atoms or asubstituted or unsubstituted aryl group having 6 to 20 carbon atoms, orT¹⁹ and T²⁰ bond to form an alkylene group which forms a lactam ringtogether with adjacent —CO—N—.

Examples of such compounds include hexylamine, heptylamine, octylamine,nonylamine, decylamine, aniline, 2-, 3- or 4-methylaniline,ethylenediamine, tetramethylenediamine, hexamethylenediamine,4,4′-diamino-1,2-diphenylethane,4,4′-diamino-3,3′-dimethyldiphenylmethane,4,4′-diamino-3,3′-diethyldiphenylmethane, dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine,N-methylaniline, piperidine, diphenylamine, triethylamine,trimethylamine, tripropylamine, tributylamine, tripentylamine,trihexylamine, triheptylamine, trioctylamine, trinonylamine,tridecylamine, methyldibutylamine, methyldipentylamine,methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine,methyldioctylamine, methyldinonylamine, methyldidecylamine,ethyldibutylamine, ethydipentylamine, ethyldihexylamine,ethydiheptylamine, ethyldioctylamine, ethydipentylamine,ethyldihexylamine, dicyclohexylmethylamine,tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine,N,N-dimethylaniline, 2,6-isopropylaniline, pyridine, 4-methylpyridine,bipyridine, 2,2′-dipyridylamine, di-2-pyridyl ketone,1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane,1,3-di(4-pyridyl)propane, 1,2-bis(2 pyridyl)ethylene,1,2-bis(4-pyridyl)ethylene, 4,4′-dipyridyl sulfide, 1,4′-dipyridyldisulfide, 1,2-bis(4-pyridyl)ethylene, 2,2′-dipicolylamine,3,3′-dipicolylamine, tetramethylammonium hydroxide,tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetra-nhexylammonium hydroxide, tetra-n-octylammonium hydroxide,phenyltrimethylammonium hydroxide, 3trifluoromethylphenyltrimethylammonium hydroxide,(2-hydroxyethyl)trimethylammonium hydroxide (so-called “choline”),N-methylpyrrolidone, and the like.

Furthermore, hindered amine compounds having piperidine skeleton asdisclosed in JP-A-H11-52575 can be used as quencher.

It is preferable that the present composition contains resin componentin an amount of about 80 to 99.9% by weight and Salt (L) in an amount of0.1 to 20% by weight on the total amount of the resin component and Salt(L).

When basic compound is used as a quencher, the basic compound iscontained preferably in an amount of about 0.01 to 1 part by weight per100 parts by weight of sum of resin component and Salt (L).

The present composition can contain, if necessary, various additives insmall amount such as a sensitizer, solution suppressing agent, otherpolymers, surfactant, stabilizer, dye and the like, as long as theeffect of the present invention is not prevented.

The present composition is usually in the form of a resist liquidcomposition in which the aforementioned ingredients are dissolved in asolvent, and the resist liquid composition is to be applied onto asubstrate such as a silicon wafer by a conventional process such as spincoating. The solvent used here is sufficient to dissolve theaforementioned ingredients, have an adequate drying rate, and give auniform and smooth coat after evaporation of the solvent and, hence,solvents generally used in the art can be used. In the presentinvention, the total solid content means total content exclusive ofsolvents.

Examples thereof include glycol ether esters such as ethyl Cellosolveacetate, methyl Cellosolve acetate and propylene glycol monomethyl etheracetate; glycol ethers such as propylene glycol monomethyl ether,di(ethylene glycol) dimethyl ether, esters such as ethyl lactate, butyllactate, amyl lactate and ethyl pyruvate and the like; ketones such asacetone, methyl isobutyl ketone, 2-heptanone and cyclohexamone; cyclicesters such as γ-butyrolactone, and the like. These solvents can be usedeach alone or in combination of two or more.

A resist film applied onto the substrate and then dried is subjected toexposure for patterning, then heat treated for facilitating a deblockingreaction, and thereafter developed with an alkali developer. The alkalideveloper used here may be any one of various alkaline aqueous solutionsused in the art, and generally, an aqueous solution oftetramethylammonium hydroxide or (2-hydroxyethyl)trimethylammoniumhydroxide (commonly known as “choline”) is often used.

It should be construed that embodiments disclosed here are examples inall aspects and not restrictive. It is intended that the scope of thepresent invention is determined not by the above descriptions but byappended claims, and includes all variations of the equivalent meaningsand ranges to the claims.

The present invention will be described more specifically by way ofexamples, which are not construed to limit the scope of the presentinvention. The “%” and “part(s)” used to represent the content of anycomponent and the amount of any material used in the following examples,and comparative examples are on a weight basis unless otherwisespecifically noted. The weight-average molecular weight of any materialused in the following examples is a value found by gel permeationchromatography [HLC-8120GPC Type, Column (Three Columns): TSK gelMultipore HXL-M, Solvent Tetrahydrofuran, manufactured by TOSOHCORPORATION] using styrene as a standard reference material. Structuresof compounds were determined by NMR (GX-270 Type, or EX-270 Type,manufactured by JEOL LTD) and mass spectrometry (Liquid Chromatography:1100 Type, manufactured by AGILENT TECHNOLOGIES LTD, Mass Spectrometry:LC/MSD Type or LC/MSD TOF Type, manufactured by AGILENT TECHNOLOGIESLTD.).

SYNTHETIC EXAMPLE 1

(Synthesis of Triphenylsulfonium4-oxo-1-adamantyloxycarbonyldifluoromethanesulfonate)

(1) 230 Parts of 30% aqueous sodium hydroxide solution was added into amixture of 100 parts of methyl difluoro(fluorosulfonyl)acetate and 250parts of ion-exchanged water in a ice bath. The added mixture was heatedand refluxed at 100° C. for 3 hours. After cooling, the cooled mixturewas neutralized with 88 parts of conc. hydrochloric acid andconcentrated to obtain 164.8 parts of sodium difluorosulfoacetate(containing inorganic salt, purity: 62.6%).(2) 5.0 Parts of sodium difluorosulfoacetate (purity: 62.8%), 2.6 partsof 4-oxo-1-adamantanol and 100 parts of ethylbenzene were charged in avessel, 0.8 parts of conc. sulfuric acid was added thereto, and themixture was refluxed for 42 hours. After cooling, the resultant mixturewas filtrated to obtain crystals, and the crystals were washed withtert-butyl methyl ether to obtain 5.5 parts of sodium salt of4-oxo-1-adamantyl difluorosulfoacetate. The purity thereof was 35.6%,which was determined by ¹H-NMR.

¹H-NMR(dimethylsulfoxide-d₆, Internal Standard:tetramethylsilane):d(ppm) 1.84 (d,2H, J=13.0 Hz); 2.00 (d, 2H, J=11.9Hz); 2.29-2.32 (m, 7H); 2.54 (s, 2H)(3) 5.4 Parts of sodium salt of 4-oxo-1-adamantyl difluorosulfoacetateobtained in (2) (purity: 35.6%) was charged in a vessel, and a mixedsolvent of 16 parts of acetonitrile and 16 parts of ion-exchanged waterwas added therein to give a mixture. A solution prepared by mixing 1.7parts of triphenylsulfonium chloride, 5 parts of acetonitrile and 5parts of ion-exchanged water was added to the mixture. After stirred for15 hours, the stirred mixture was concentrated and extracted with 142parts of chloroform. The organic layer was washed with ion-exchangedwater. The obtained organic layer was concentrated. The concentrate waswashed with 24 parts of tert-butyl methyl ether and the solvent wasdecanted and the crystals was dried to obtain 1.7 parts oftriphenylsulfonium 4-oxo-1-adamantyloxycarbonyldifluoromethanesulfonate,which is called as acid generator B1.

¹H-NMR(dimethylsulfoxide-d₆, Internal Standard;tetramethylsilane):d(ppm) 1.83 (d, 2H, J=12.7 Hz); 2.00 (d, 2H, J=12.0Hz); 2.29-2.32 (m, 7H); 2.53 (s, 2H); 7.75-7.91 (m, 15H)MS (ESI(+) Spectrum): M+263.2 (C₁₈H₁₅S⁺=2.63.09)MS (ESI(−) Spectrum): M−323.0 (C₁₂H₁₃F₂O₆S⁻=323.04)

SYNTHETIC EXAMPLE 2

(Synthesis of Triphenylsulfonium4-hydroxy-1-adamantyloxycarbonyldifluoromethanesulfonate)

(1) 4.69 Parts of triphenylsulfonium4-oxo-1-adamantyloxycarbonyldifluoromethanesulfonate was dissolved in 15parts of acetonitrile. Into the solution was added dropwise a solutionobtained by dissolving 0.15 part of sodium borohydride in 1.51 parts ofion-exchanged water. After the added mixture was stirred for 5 hours, 1Nhydrochloric acid was added thereto, and extracted with 1.13 parts ofchloroform. After repeatedly washed with ion exchanged water, theorganic layer obtained was concentrated. To the concentrate,acetonitrile was added, then the added mixture was concentrated. Theconcentrate was added dropwise into ethyl acetate. The mixture wasfiltrated to obtain solid. The solid was dried to obtain 2.20 parts oftriphenylsulfonium4-hydroxy-1-adamantyloxycarbonyldifluoromethanesulfonate in the form ofwhite solid, which is called as acid generator B2. As a result ofanalyses by ¹H-NMR and LCMS, the acid generator B2 determined to be amixture of two isomers.

¹H-NMR spectrum thereof is shown in FIG. 1.MS (ESI(+) Spectrum): M+263.0 (C₁₈H₁₅S³⁰=263.09)MS (ESI(−) Spectrum): M−325.0 (C₁₂H₁₃F₂O₆S⁻=325.06)

SYNTHETIC EXAMPLE 3

(Synthesis of 1-(2-oxo-2-phenylethyl)tetrahydrothiophenium4-oxo-1-adamantyloxycarbonyldifluoromethanesulfonate)

10 Parts of sodium slat of 4-oxo-1-adamantyl difluorosulfoacetate(purity: 55.2%) was charged in a vessel, and a mixed solvent of 30 partsof acetonitrile and 20 parts of ion-exchanged water was added thereto togive a mixture. A solution prepared by mixing 5.0 parts of1-(2-oxo-2-phenylethyl)tetrahydrothiophenium bromide, 10 parts ofacetonitrile and 20 parts of ion exchanged water was added to themixture. After stirred for 15 hours, the stirred mixture wasconcentrated and extracted with 98 parts of chloroform. The organiclayer was washed with ion-exchanged water. The obtained organic layerwas concentrated. The concentrate was washed with 70 parts of ethylacetate and the solvent was decanted and the crystals was dried toobtain 5.2 parts of 1-(2-oxo-2-phenylethyl)tetrahydrothiophenium4-oxo-1-adamantyloxycarbonyldifluoromethanesulfonate in the form ofwhite solid, which is called as acid generator B3.

¹H-NMR(dimethylsulfoxide-d₆, Internal Standard: Tetramethylsilane):δ(ppm) 1.83 (d, 2H, J=12.5 Hz); 2.00 (d, 2H, J=12.0 Hz); 2.21-2.37 (m,11H); 2.53 (s, 2H); 3.47-3.62 (m, 4H); 5.31 (s, 2H); 7.63 (t, 2H, J=7.3Hz); 7.78 (t, 1H, J=7.6 Hz); 8.01 (dd, 2H, J=1.5 Hz, 7.3 Hz)MS (ESI(+) Spectrum): M+207.1 (C₁₂H₁₅O S⁺=207.08)MS (ESI(−) Spectrum): M−323.0 (C₁₂H₁₃F₂O₆S⁻=323.04)

REFERENTIAL SYNTHETIC EXAMPLE 1

(Synthesis of Triphenylsulfonium1-adamantylmethoxycarbonyldifluoromethanesulfonate)

(1) 230 Parts of 30% aqueous sodium hydroxide solution was added into amixture of 100 parts of methyl difluoro(fluorosulfonyl)acetate and 250parts of ion-exchanged water in a ice bath. The added mixture was heatedand refluxed at 100° C. for 3 hours. After cooling, the cooled mixturewas neutralized with 88 parts of conc. hydrochloric acid andconcentrated to obtain 164.8 parts of sodium difluorosulfoacetate(containing inorganic salt, purity: 62.6%).(2) 39.4 Parts of sodium difluorosulfoacetate (purity: 63.5%), 21.0parts of 1-adamantanemethanol and 200 parts of dichloroethane werecharged in a vessel, 24.0 parts of p-toluenesulfonic acid was addedthereto, and the mixture was refluxed for 7 hours. After concentratingthe mixture to eliminate dichloroethane, 250 parts of tert butyl methylether was added thereto, and the added mixture was stirred. The stirredmixture was filtered to obtain solid. 250 parts of acetonitrile wasadded to the solid. The mixture was stirred and filtrated. The filtratewas concentrated to obtain 32.8 parts of sodium salt of1-adamantylmethyl difluorosulfoacetate.

(3) 32.8 parts of sodium salt of 1-adamantylmethyl difluorosulfoacetateobtained in (2) was dissolved in 100 parts of ion-exchanged water. 28.3Parts of triphenylsulfonium chloride and 140 parts of methanol wereadded to the solution. After stirred for 15 hours, the stirred mixturewas concentrated and extracted with 200 parts of chloroform twice. Theorganic layers were mixed and washed with ion-exchanged water. Theobtained organic layer was concentrated. 300 Part of tert-butyl methylether was added to the concentrate, the mixture was stirred filtered toobtain solid. The solid was dried under reduced pressure to obtain 39.7parts of triphenylsulfonium1-adamantylmethoxycarbonyldifluoromethanesulfonate in the form of whitecrystals, which is called as acid generator C1.

¹H-NMR (dimethylsulfoxide-d₆, Internal Standard: tetramethylsilane):d(ppm) 1.52(d, 6H); 1.63(dd, 6H); 1.93(s, 3H); 3.81(s, 2H); 7.76-7.90(m,15H)MS (ESI(+) Spectrum): M+263.2 (C₁₈H₁₅O S⁺=263.09)MS (ESI(−) Spectrum): M−323.0 (C₁₃H₁₇F₂O₅S⁻=323.08)

RESIN SYNTHESIS EXAMPLE 1 (SYNTHESIS OF RESIN A1)

2-Ethyl-2-adamantyl methacrylate, 3-hydroxy-1-adamantyl methacrylate andα-methacryloyloxy-γ-butyrolactone were charged at a molar ratio of5:2.5:2.5 (20.0 parts:9.5 parts:73 parts), and methyl is isobutyl ketonein twice weight based on all monomers was added, to prepare solution. Tothe solution was added azobisisobutyronitrile as an initiator in a ratioof 2 mol % based on all monomer molar amount, and the mixture was heatedat 80° C. for about 8 hours. Then, the reaction solution was poured intolarge amount of heptane to cause precipitation, and this operation wasrepeated three times for purification. As a result, copolymer having aweight-average molecular weight of about 9,200 was obtained. This iscalled resin A1.

EXAMPLES 1 TO 2 AND COMPARATIVE EXAMPLES 1 TO 2

The following components were mixed and dissolved, further, filtratedthrough a fluorine resin filter having pore diameter of 0.2 μm, toprepare resist liquid.

<Resin>

resin A1: 10 parts

<Acid Generator>

acid generator B1: 0.25 part

acid generator B2: 0.26 part

acid generator C1: 0.26 part

acid generator C2: triphenyl sulfonium perfluorobutanesulfonate 0.25partKind used in Examples is described in Table 1<Quencher>quencher Q1: 2,6-diisopropylaniline 0.0325 part

<Solvent> Solvent Y1: propylene glycol monomethyl ether acetate 51.5parts 2-heptanone 35.0 parts γ-butyrolactone  3.5 parts

Silicon wafers were each coated with “ARC-29A-8”, which is an organicanti-reflective coating composition available from Brewer Co., and thenbaked under the conditions: 215° C., 60 seconds, to form a 780 Å-thickorganic anti-reflective coating. Each of the resist liquids prepared asabove was spin-coated over the anti-reflective coating so that thethickness of the resulting film became 0.25 μm after drying. The siliconwafers thus coated with the respective resist liquids were each prebakedon a direct hotplate at a temperature of 130° C. for 60 seconds. Usingan ArF excimer stopper (“NSR ArF” manufactured by Nikon Corporation,NA=0.55, 2/3 Annular), each wafer thus formed with the respective resistfilm was subjected to line and space pattern exposure, with the exposurequantity being varied stepwise.

After the exposure, each wafer was subjected to post-exposure baking ona hotplate at a temperature of 130° C. for 60 seconds, and then topaddle development for 60 seconds with an aqueous solution of 2.38 wt %tetramethylammonium hydroxide.

Each of a dark field pattern developed on the organic anti-reflectivecoating substrate after the development was observed with a scanningelectron microscope, the results of which are shown in Table 1. The term“dark field pattern”, as used herein, means a pattern obtained byexposure and development through a reticle comprising chromium basesurface (light shielding portion) and linear glass layers(light-transmitting portion) formed in the chromium surface and alignedwith each other. Thus, the dark field pattern is such that, afterexposure and development, resist layer surrounding the line and spacepattern remains on substrate.

Resolution:

It is expressed as the minimum size of space pattern which gave thespace pattern split by the line pattern at the exposure amount of theeffective sensitivity. Herein, the effective sensitivity is expressed bythe amount of exposure that the line pattern (light-shielding layer) andthe space pattern (light-transmitting layer) become 1:1 after exposurethrough 0.13 μm line and space pattern mask and development.

Profile T/B

It is expressed by a ratio of top side length (referred to as T) andbottom side length (referred to as B) in line part of 0.13 μm line andsaid space pattern. The closer to 1 the ratio is, the better the profileof its resist pattern is. TABLE 1 No. Acid Generator Resolution (μm)Profile T/B Example 1 B1 0.12 1.00 Example 2 B2 0.12 1.04 Comparative C10.13 0.86 Example 1 Comparative C2 0.13 0.71 Example 2

Apparent from Table 1, the resist compositions of Examples, which accordto the present invention, give better resist pattern in resolution andin pattern profile than those of Comparative Examples.

Salt (L) is suitably used for an acid generator for chemically amplifiedpositive resist composition. The present composition provides excellentresist pattern in resolution and pattern profiles and is especiallysuitable for ArF excimer laser lithography, KrF excimer laserlithography and ArF immersion lithography.

1. A salt of the formula (L):

wherein Q represents —CO— group or —C(OH)— group; ring x representsmonocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atomsin which a hydrogen atom is substituted with a hydroxyl group at Qposition when Q is —C(OH)— group or in which two hydrogen atoms aresubstituted with ≡O group at Q position when Q is —CO— group, and atleast one hydrogen atom in the monocyclic or polycyclic hydrocarbongroup may optionally be substituted with alkyl group having 1 to 6carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkylgroup having 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰ eachindependently represent fluorine atom or perfluoroalkyl group having 1to 6 carbon atoms; and A⁺ represents organic counter ion.
 2. The saltaccording to claim 1, wherein each of R¹⁰ and R²⁰ is fluorine atom ortrifluoromethyl group.
 3. The salt according to claim 1, wherein thesalt is the one of the formula (I)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined in claim 1.4. The salt according to claim 1, wherein the salt is the one of theformula

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined in claim 1.5. The salt according to claim 1, wherein A⁺ is at least one cationselected from the group consisting of the formula (IIIa), the formula(IIb), the formula (IIIc) and the formula (IIId). A cation of theformula (IIIa)

wherein P¹, P² and P³ each independently represent hydrogen atom,hydroxyl group, alkyl group having 1 to 12 carbon atoms or alkoxy grouphaving 1 to 12 carbon atoms. A cation of the formula (IIIb)

wherein P⁴ and P⁵ each independently represent hydrogen atom, hydroxylgroup, alkyl group having 1 to 12 carbon atoms or alkoxy group having 1to 12 carbon atoms. The formula (IIIc)

wherein P⁶ and P⁷ each independently represent alkyl having 1 to 12carbon atoms or cycloalkyl having 3 to 12 carbon atoms, or P⁶ and P⁷bond to form divalent acyclic hydrocarbon group having 3 to 12 carbonatoms which forms a ring together with the adjacent S*, and at least one—CH₂— in the divalent acyclic hydrocarbon group is optionallysubstituted by —CO—, —O— or —S—, P⁸ represents hydrogen, P⁹ representsalkyl having 1 to 12 carbon atoms, cycloalkyl having 3 to 12 carbonatoms or aromatic ring group optionally substituted, or P⁸ and P⁹ bondto form divalent acyclic hydrocarbon group which forms 2-oxocycloalkyltogether with the adjacent —CHCO—, and at least one —CH₂— in thedivalent acyclic hydrocarbon group is optionally substituted by —CO—, —Oor —S—, A cation of the formula (IIId)

wherein P¹⁰, P¹¹, P¹², P¹³, P¹⁴, P¹⁵, P¹⁶, P¹⁷, P¹⁸, P¹⁹, P²⁰ and P²¹each independently represent hydrogen atom, hydroxyl group, alkyl grouphaving 1 to 12 carbon atoms or alkoxy group having 1 to 12 carbon atoms,B represents sulfur atom or oxygen atom, and m represents 0 or
 1. 6. Thesalt according to claim 1, wherein A⁺ is a counter ion of the formula(IIIe):

wherein P²², P²³ and P²⁴ each independently represent hydrogen atom oralkyl group having 1 to 4 atoms.
 7. The salt according to claim 1,wherein the ring X is cycloalkyl group having 4 to 8 carbon atoms,adamantyl group or norbornyl group, provided that, in each of the group,a hydrogen atom is substituted with —OH group at Q position when Q is—C(OH)— group and two hydrogen atoms are substituted with ≡O at Qposition when Q is —CO— group, and provided that at least one hydrogenatom in each of the group may optionally be substituted with alkyl grouphaving 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms,perfluoroalkyl group having 1 to 4 carbon atoms, hydroxyalkyl grouphaving 1 to 6 carbon atoms, hydroxyl group or cyano group.
 8. The saltaccording to claim 6, wherein the salt is one of the formula (IVa)

wherein P²⁵, P²⁶ and P²⁷ each independently represent hydrogen atom,alkyl group having 1 to 4 carbon atom.
 9. The salt according to claim 6,wherein the salt is the one of the formula (IVa)

wherein P²⁵, P²⁶ and P²⁷ have the same meanings as defined in claim 8.10. A salt of the formula (LI)

wherein Q represents —CO— group or —C(OH)— group; X representsmonocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atomsin which a hydrogen atom is substituted with a hydroxyl group at Qposition when O is —C(OH)— group or in which two hydrogen atoms aresubstituted with ≡O group at Q position when Q is —CO— group, and atleast one hydrogen atom in the monocyclic or polycyclic hydrocarbongroup may optionally be substituted with alkyl group having 1 to 6carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkylgroup having 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰ eachindependently represent fluorine atom or perfluoroalkyl group having 1to 6 carbon atoms; and M represents Li, Na, K or Ag.
 11. The saltaccording to claim 10, wherein the salt has the formula (V)

wherein X, R¹⁰, R²⁰ and M have the same meanings as defined in claim 10.12. The salt according to claim 10, wherein the salt has the formula(VI)

wherein X, R¹⁰, R²⁰ and M have the same meanings as defined in claim 10.13. (canceled)
 14. A process for producing a salt of the formula (II)

wherein ring X represents monocyclic or polycyclic hydrocarbon grouphaving 3 to 30 carbon atoms in which a hydrogen atom is substituted witha hydroxyl group at Q position when Q is —C(OH)— group or in which twohydrogen atoms are substituted with ≡O group at Q position when Q is—CO— group, and at least one hydrogen atom in the monocyclic orpolycyclic hydrocarbon group may optionally be substituted with alkylgroup having 1 to 6 carbon atom, alkoxy group having 1 to 6 carbon atom,perfluoroalkyl group having 1 to 4 carbon atoms, hydroxyalkyl grouphaving 1 to 6 carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰each independently represent fluorine atom or perfluoroalkyl grouphaving 1 to 6 carbon atoms; and A⁺ represents organic counter ion, whichcomprises reducing a salt of the formula (I)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined above.15-16. (canceled)
 17. A process for producing a salt of the formula (L)

wherein Q represents —CO— group or —C(OH)— group; ring X represents amonocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atomsin which a hydrogen atom is substituted with a hydroxyl group at Qposition when Q is —C(OH)— group or in which two hydrogen atoms aresubstituted with ≡O group at Q position when Q is —CO— group, and atleast one hydrogen atom in the monocyclic or polycyclic hydrocarbongroup may optionally be substituted with alkyl group having 1 to 6carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkylgroup having 1 to 4 carbon atoms, hydroxyalkyl group having 1 to 6carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰ eachindependently represent fluorine atom or perfluoroalkyl group having 1to 6 carbon atoms; and A* represents organic counter ion, whichcomprises reacting a salt of the formula (LI)

wherein M represents Li, Na, K or Ag, and O, R¹⁰, R²⁰ and X have thesame meanings as defined above, with a compound of the formula (XI)A⁺Z⁻  (XI) wherein Z represents F, Cl, Br, I, BF₄, AsF₆, SbF₆, PF₆, orC10₄, and A⁺ has the same meaning as defined above.
 18. A chemicallyamplified resist composition comprising a salt of the formula (L)

wherein Q represents —CO— group or —C(OH)— group, ring X representsmonocyclic or polycyclic hydrocarbon group having 3 to 30 carbon atomsin which a hydrogen atom is substituted with a hydroxyl group at Qposition when Q is —C(OH)— group or in which two hydrogen atoms aresubstituted with ≡O group at Q position when Q is —CO— group, and atleast one hydrogen atom in the monocyclic or polycyclic hydrocarbongroup may optionally be substituted with alkyl group having 1 to 6carbon atom, alkoxy group having 1 to 6 carbon atom, perfluoroalkylgroup having 1 to 4 carbon atoms, hydroxyalkyl group having I to 6carbon atoms, hydroxyl group or cyano group; R¹⁰ and R²⁰ eachindependently represent fluorine atom or perfluoroalkyl group having 1to 6 carbon atoms; and A⁺ represents organic counter ion, and a resinwhich contains a structural unit having an acid-labile group and whichitself is insoluble or poorly soluble in an alkali aqueous solution butbecomes soluble in an alkali aqueous solution by the action of an acid.19. The composition according to claim 18, wherein each of R¹⁰ and R²⁰is fluorine atom or trifluoromethyl group.
 20. The composition accordingto claim 18, wherein the resin contains a structural unit derived from amonomer having a bulky and acid-labile group.
 21. The compositionaccording to claim 20, wherein the bulky and acid-labile group is2-alkyl-2-adamantyl group or 1-(1-adamantyl)-1-alkylalkyl group.
 22. Thecomposition according to claim 20, wherein the monomer having bulky andacid-labile group is 2-alkyl-2-adamantyl(meth)acrylate,1-(1-adamantyl)-1-alkylalkyl(meth)acrylate,2-alkyl-2-adamantyl-5-norbornene-2-carboxylate,1-(1-adamantyl)-1-alkylalkyl-5-norbornene-2-carboxylate,2-alkyl-2-adamantyl α-chloroacrylate or 1-(1-adamantyl)-1-alkylalkylα-chloroacrylate.
 23. The composition according to claim 18, wherein thecomposition further comprises a basic compound.
 24. The salt accordingto claim 18, wherein the salt has the following formula (I)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined in claim 18.25. The composition according to claim 18, wherein the salt has thefollowing formula (II)

wherein X, A, R¹⁰ and R²⁰ have the same meanings as defined in claim 18.26. The composition according to claim 18, wherein A⁺ is at least onecation selected from the group consisting of the formula (IIIa), theformula (IIIb), the formula (IIIc) and the formula (IIId). A cation ofthe formula (IIIa)

wherein P¹, P² and P³ each independently represent hydrogen atom,hydroxyl group, alkyl group having 1 to 12 carbon atoms or alkoxy grouphaving 1 to 12 carbon atoms. A cation of the formula (IIIb)

wherein P⁴ and P⁵ each independently represent hydrogen atom, hydroxylgroup, alkyl group having 1 to 12 carbon atoms or alkoxy group having 1to 12 carbon atoms. The formula (IIIc)

wherein P⁶ and P⁷ each independently represent alkyl having I to 12carbon atoms or cycloalkyl having 3 to 12 carbon atoms, or P⁶ and P⁷bond to form divalent acyclic hydrocarbon group having 3 to 12 carbonatoms which forms a ring together with the adjacent S*, and at least one—CH₂— in the divalent acyclic hydrocarbon group is optionallysubstituted by —CO—, —O— or —S—, P⁸ represents hydrogen, P⁹ representsalkyl having 1 to 12 carbon atoms, cycloalkyl having 3 to 12 carbonatoms or aromatic ring group optionally substituted, or P⁸ and P⁹ bondto form divalent acyclic hydrocarbon group which forms 2-oxocycloalkyltogether with the adjacent —CHCO—, and at least one —CH₂- in thedivalent acyclic hydrocarbon group is optionally substituted by —CO—,—O—, or —S—. A cation of the formula (IIId)

wherein P¹⁰, P¹¹, P¹², P¹³, P¹⁴, P¹⁵, P¹⁶, P¹⁷, P1⁸, P¹⁹, P²⁰ and P²¹each independently represent hydrogen atom, hydroxyl group, alkyl grouphaving 1 to 12 carbon atoms or alkoxy group having 1 to 12 carbon atoms,B represents sulfur atom or oxygen atom, and m represents 0 or
 1. 27.The composition according to claim 26, wherein A⁺ is a counter ion ofthe formula (IIIe):

wherein P²², P²³ and P²⁴ each independently represent hydrogen atom oralkyl group having 1 to 4 carbon atoms.
 28. The composition according toclaim 18, wherein the ring X is cycloalkyl group having 4 to 8 carbonatoms, adamantyl group or norbornyl group, provided that, in each of thegroup, a hydrogen atom is substituted with —OH group at Q position whenQ is —C(OH)— group and two hydrogen atoms are substituted with ≡O at Qposition when Q is —CO— group, and provided that at least one hydrogenatom in each of the group may optionally be substituted with alkyl grouphaving 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms,perfluoroalkyl group having 1 to 4 carbon atoms, hydroxyalkyl grouphaving 1 to 6 carbon atoms, hydroxyl group or cyano group.
 29. Thecomposition according to claim 27, wherein the salt is the one of theformula (IVa)

wherein P²⁵, P²⁶ and P²⁷ each independently represent hydrogen atom,alkyl group having 1 to 4 carbon atom.
 30. The composition according toclaim 27, wherein the salt is one of the formula (IVb)

wherein P²⁵, P²⁶ and P²⁷ have the same meanings as defined in claim 29.